Field
The present disclosure relates generally to zero sequence ground current sensing apparatuses and methods. More specifically, the present disclosure relates to apparatuses and methods for ascertaining phase faults associated with the multiphase power systems.
Description of Related Art
Current transformers (CTs) are known apparatuses for detecting phase line or conductor failures. Specifically, a common CT is a toroidal magnetic core that includes a window that encloses one or more phase lines or conductors. The magnetic core is wrapped with multiple turns of a second conductor, known as the “secondary”, that when properly terminated will produce a current proportional to the flux experienced by the magnetic core. Another name for a CT intended to measure the resulting summation of multiple different phase conductors is a zero sequence CT.
Under normal load conditions, a vector sum of the phase currents associated with the phase lines or conductors passing through the CT's window will be zero or close to zero. When the vector sum of the phase currents is zero or close to zero, flux is not introduced in the core of the CT. However, if one or more of the phase lines or conductors passing through the CT allows current to pass in a conduction path outside of the CT, the vector sum of the phase currents associated the phase lines or conductors passing through the CT's window will no longer be zero. When the vector sum of the phase currents is no longer zero, a flux is introduced in the core of the CT. The flux will induce a current in the CT's secondary. The current of sufficient magnitude may be communicated to an auxiliary relay. The auxiliary relay may be coupled to a circuit breaker, alarm, or other circuit disrupting device. The circuit-disrupting device may be arranged to terminate voltage flowing on the phase lines or conductors passing through the CT.
Known CTs have various drawbacks. First, known CTs are difficult to install. For example, most high accuracy CTs make use of a contiguous magnetic core window. Therefore, installation of known CTs necessitates having to feed the phase line conductors through the contiguous window. This makes it difficult to install known CTs on already deployed phase line conductors. Second, known CTs are quite large in size. Therefore, the size of known CTs may restrict their deployment locations, or add cost to provide space for their installation. Finally, for proper operation phase line conductors must be properly positioned and centered within the window of known CTs. Therefore, it is often necessary to mount known CTs and phase line conductors to rigid support structures on either or both sides of the known CT. Use of such rigid support structures may increase the deployment costs associated with the use of CTs. Finally, known CTs require that all conductors must pass thru them perpendicular to the core window, and that no bends of conductors are allowed within a specified distance of the core to maintain accuracy.
Other problems with known CTs will become apparent in view of the disclosure below.